JP3702838B2 - Spark plug and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spark plug in which a center electrode and a ground electrode are arranged to face each other via a discharge gap, and a noble metal tip is laser-welded to a portion of the ground electrode facing the discharge gap, and a method for manufacturing the spark plug.
[0002]
[Prior art]
This type of spark plug is used as an ignition plug for an internal combustion engine, but from the viewpoint of exhaust purification and lean combustion, wear resistance such as Pt (platinum) alloy or Ir (iridium) alloy on the electrode surface facing the discharge gap. A noble metal tip made of an excellent noble metal is provided, thereby improving ignitability and durability.
[0003]
Here, as a measure for improving the bondability between the electrode base material and the noble metal tip, conventionally, there has been a technique using laser welding as described in JP-A-11-233233 and JP-A-9-106880. Proposed.
[0004]
In the former publication, the tip of the electrode base material is thinned, and a noble metal tip is laser welded to the thinned portion. In the latter publication, a noble metal tip is embedded in the electrode base material and an electrode is placed around the tip. A raised portion of the base material is formed, and this raised portion and the tip are laser welded.
[0005]
[Problems to be solved by the invention]
However, according to the study by the present inventors, when the technique described in the above-mentioned conventional publication is used, in the joining between the center electrode and the noble metal tip, it is possible to ensure a practical level of connectivity, but the ground electrode and the noble metal tip. It was found that in the joining, peeling occurred from the joining portion and the worst chip dropped off.
[0006]
This is because the ground electrode protrudes into the combustion chamber as compared with the center electrode in the form of attachment of the spark plug to the internal combustion engine, whereby the ground electrode has a higher electrode temperature than the center electrode, This is because the thermal stress generated between the noble metal tip and the electrode base material, that is, in the melted portion, is increased.
[0007]
For this reason, when laser welding the noble metal tip to the ground electrode, it is necessary to make the bondability better than the conventional method described above. However, in order to improve the bondability between the noble metal tip and the ground electrode, it is necessary to consider not only the bondability but also the ignitability.
[0008]
Therefore, in view of the above problems, the present invention aims to improve the bondability between the ground electrode and the noble metal tip while appropriately ensuring the ignitability in the spark plug formed by laser welding the noble metal tip to the ground electrode. To do.
[0009]
[Means for Solving the Problems]
The inventors of the present invention have conducted intensive studies on ensuring the above ignitability and improving the bondability. First, with regard to ignitability, focusing on the fact that the precious metal tip has a smaller diameter and a longer protrusion length from the ground electrode, the more difficult it is to inhibit the growth of flame nuclei generated in the discharge gap. An experimental study was conducted on the diameter of the noble metal tip and the protruding length from the ground electrode, which can ensure good ignitability without hindering the growth of the nucleus.
[0010]
In addition, regarding the bondability between the ground electrode and the noble metal tip, when the laser welding structure of the noble metal tip according to the conventional method described above is applied to the center electrode, the thermal stress generated at the melted portion between the center electrode and the tip (on the center electrode side) The thermal stress was considered as a standard. This is because, as described above, if the level of the central electrode side thermal stress generated by the conventional method is used, the bondability between the electrode base material and the chip at a practical level can be secured.
[0011]
If the laser welding structure between the ground electrode and the tip is realized so that the thermal stress of the melted portion (ground electrode side thermal stress) in the laser welding structure between the ground electrode and the tip does not exceed the center electrode side thermal stress. I thought that the above-mentioned purpose could be achieved.
[0012]
Here, in the spark plug of the above-mentioned conventional publication, when the cross section along the axial direction of the tip in the melted portion is viewed, the outer surface of the melted portion connecting the side surface of the noble metal tip and the joint surface of the noble metal tip in the electrode base material is a straight line. (See FIG. 3). If the melted part is made thinner than such a melted part shape, the thermal stress generated in the melted part can be reduced and the bondability between the ground electrode and the noble metal tip can be improved. Thought.
[0013]
The present invention has been made on the basis of the above-described studies on ensuring ignitability and improving bondability.
[0014]
That is, in the invention described in claim 1, the noble metal tip (45) is laser-welded at one end to the ground electrode (40), and the cross-sectional area of the tip surface at the other end is 0.12 mm. ² 1.15mm above ² The protrusion length (L) from the ground electrode is not less than 0.3 mm and not more than 1.5 mm, and in the melting part (47) where the ground electrode and the noble metal tip are melted together, the side surface (45a) of the noble metal tip and An outer surface (47a) connecting the joint surface (43) of the noble metal tip in the ground electrode, It is a concave curved shape and has a radius of curvature (R) of 0.1 mm or more and 1.0 mm or less. It is characterized by that.
[0015]
As a result of an experimental study on the relationship between the above-described ignitability, the diameter of the noble metal tip and the protruding length from the ground electrode, the cross-sectional area of the laser-welded tip surface on the other end side is 1.15 mm. ² It has been confirmed experimentally that a good ignitability can be secured without hindering the growth of the flame kernel if the noble metal tip has a protrusion length (L) from the ground electrode of 0.3 mm or more.
[0016]
On the other hand, in the noble metal tip, the cross-sectional area is 0.12 mm. ² If it is thinner, the sparks are concentrated and the wearability is deteriorated, and if the protrusion length from the ground electrode is longer than 1.5 mm, the temperature at the tip of the chip is greatly increased and it becomes easy to melt. Therefore, if the noble metal tip has a cross-sectional area and a protruding length from the ground electrode as in the present invention, the ignitability can be appropriately ensured.
[0017]
Further, as a result of studying the shape of the melted portion in order to reduce the thermal stress generated in the melted portion, the side surface (45a) of the noble metal tip (45) and the joint surface (43) of the noble metal tip in the ground electrode (40) are connected. If the outer surface (47a) of the melted part (47) has a curved surface shape with a radius of curvature (R), the melted part is as thin as possible while securing the volume required for joining in the melted part. I thought it was possible.
[0018]
And when it actually analyzed about the fusion | melting part which makes the said shape, it has confirmed that the thermal stress which generate | occur | produces in the said fusion | melting part can be suppressed below to the central electrode side thermal stress which generate | occur | produces by the conventional method.
[0019]
Therefore, according to the present invention made on the basis of the above examination results, it is possible to provide a spark plug in which the joining property between the ground electrode and the noble metal tip is improved while appropriately ensuring the ignitability.
[0020]
Furthermore, when the curvature radius (R) in the melted part (47) according to claim 1 is analyzed based on the center electrode side thermal stress generated by the conventional method, the curvature radius is smaller than 0.1 mm. It was also found that if it is larger than 1.0 mm, the thermal stress applied to the melted part tends to exceed the level of the central electrode side thermal stress (see FIG. 8A).
[0021]
From this, The invention according to claim 1 is characterized in that the radius of curvature (R) is not less than 0.1 mm and not more than 1.0 mm. in this case, Laser welding of precious metal tip (45) to ground electrode (40) Shi When trying to reduce the radius of curvature (R), the penetration depth (d) of the melting part (47) becomes insufficient (see FIG. 8B).
[0022]
Therefore, as a result of experiments and analysis, the radius of curvature (R) is set to D as the maximum width of the cross section in contact with the ground electrode (40) of the noble metal tip (45) as in the invention described in claim 2. In order to ensure the bondability of the noble metal tip while exhibiting the effect of the first aspect of the invention, it is preferable that the range is D / 4 or more and 3D / 4 or less.
[0023]
The inventions according to claims 3 to 6 provide a specific configuration of the noble metal tip according to claim 1 or claim 2. The invention described in claim 3 is an alloy containing Ir as a main component and at least one of Rh, Pt, Ni, W, Pd, Ru, and Os added thereto.
[0024]
More specifically, as in the invention described in claim 4, the noble metal tip (45) is mainly composed of Ir, 50% by weight Rh, 50% by weight Pt, 40% by weight Ni or less. , 30 wt% or less of W, 40 wt% or less of Pd, 30 wt% or less of Ru, and 20 wt% or less of Os.
[0025]
Further, as in the invention described in claim 5, the noble metal tip (45) is such that the noble metal tip (45) contains Pt as a main component and at least one of Ir, Ni, Rh, W, Pd, Ru, and Os is added. It may be an alloy that has been made.
[0026]
More specifically, as in the invention described in claim 6, the noble metal tip (45) is mainly composed of Pt, 50 wt% or less of Ir, 40 wt% or less of Ni, and 50 wt% or less of Rh. , 30 wt% or less of W, 40 wt% or less of Pd, 30 wt% or less of Ru, and 20 wt% or less of Os.
[0027]
By employing the above-described noble metal tip, a noble metal tip having a high melting point composition with excellent wear resistance can be realized, and a sufficient life can be secured even in an engine with a severe heat load in the future. Further, the inventions of the first and second aspects of the invention appropriately exhibit effects even when such a noble metal tip is employed.
[0028]
When such an Ir alloy tip or a Pt alloy tip was used as the noble metal tip, the components of the noble metal tip in the melting part were analyzed. As a result, as in the invention described in claim 7, if the component of the noble metal tip (45) in the melted part (47) is 35 wt% or more and 80 wt% or less, the thermal stress applied to the melted part is determined as a reference. It was found that the above-mentioned center electrode side thermal stress can be suppressed to a level not exceeding.
[0029]
The definition of the component ratio of the noble metal tip in the molten part here is as follows. Component analysis is performed on 10 areas of a 50 μm square area at an arbitrary position in the melting portion, and the average value is obtained. In laser welding, the component ratio is not actually uniform and varies somewhat. However, according to the method of taking the average value at 10 locations, the entire composition can be regarded as a uniform composition. Confirmed by evaluation.
[0032]
In addition, the code | symbol in the bracket | parenthesis of each said means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below. FIG. 1 is a half sectional view showing the overall configuration of a spark plug S1 according to an embodiment of the present invention. This spark plug S1 is applied to a spark plug of an automobile engine, and is inserted and fixed in a screw hole provided in an engine head (not shown) that defines a combustion chamber of the engine. It is like that.
[0034]
The spark plug S1 has a cylindrical mounting bracket 10 made of a conductive steel material (eg, low carbon steel), and the mounting bracket 10 is a mounting screw portion for fixing to an engine block (not shown). 11 is provided. The mounting bracket 10 has an alumina ceramic (Al ₂ O _Three ) Or the like is fixed, and a tip portion 21 of the insulator 20 is provided so as to be exposed from one end of the mounting bracket 10.
[0035]
A center electrode 30 is fixed to the shaft hole 22 of the insulator 20, and the center electrode 30 is insulated and held with respect to the mounting bracket 10. The center electrode 30 is, for example, a cylindrical body made of a metal material having excellent heat conductivity such as Cu as an inner material and a metal material having excellent heat resistance and corrosion resistance such as a Ni-based alloy as shown in FIG. Thus, the tip surface 31 is provided so as to be exposed from the tip portion 21 of the insulator 20.
[0036]
On the other hand, the ground electrode 40 is composed of, for example, a prism made of a Ni-based alloy containing Ni as a main component. The ground electrode 40 is fixed to one end of the mounting bracket 10 at the root end portion 42 by welding, and is substantially L-shaped in the middle. It is bent and faces the front end surface 31 of the center electrode 30 via the discharge gap 50 on the side surface 43 (hereinafter referred to as the front end portion side surface) 43 of the front end portion 41.
[0037]
Here, FIG. 2 shows an enlarged configuration near the discharge gap 50 in the spark plug S1. As described above, the distal end surface 31 of the center electrode 30 and the distal end side surface 43 of the ground electrode 40 are arranged to face each other via the discharge gap 50, and the discharge gap 50 at the center and the ground electrodes 30, 40 faces the discharge gap 50. Noble metal tips 35 and 45 are joined to the portions 31 and 43 to be welded by laser welding.
[0038]
That is, a noble metal tip (hereinafter referred to as a center electrode side tip) 35 is provided on the distal end surface 31 of the center electrode 30, and a noble metal tip (hereinafter referred to as a ground electrode side tip) is provided on the distal end side surface 43 of the ground electrode 40. 45 are each welded. Both of these tips are cylindrical, and one end face side thereof is laser welded to the electrodes 30 and 40. And the discharge gap 50 is a space | gap between the front-end | tip parts of both the chips | tips 35 and 45, for example, is about 0.7 mm.
[0039]
These chips 35 and 45 may be made of a noble metal such as Pt, Pt alloy, Ir, or Ir alloy. For example, an Ir alloy chip containing Ir as a main component and at least one of Rh, Pt, Ni, W, Pd, Ru, Os added, or Ir, Ni, Rh, W, Pd, Ru, Os containing Pt as a main component. A Pt alloy chip to which at least one of the above is added can be obtained.
[0040]
More specifically, the Ir alloy chip includes Ir as a main component, 50% by weight Rh, 50% by weight Pt, 40% by weight Ni, 30% by weight W, 40% by weight or less. Pd, 30 wt% or less of Ru, and 20 wt% or less of Os can be added to the alloy.
[0041]
The Pt alloy chip includes Pt as a main component, 50 wt% or less of Ir, 40 wt% or less of Ni, 50 wt% or less of Rh, 30 wt% or less of W, 40 wt% or less of Pd, It may be an alloy to which at least one of 30 wt% or less of Ru and 20 wt% or less of Os is added.
[0042]
In this example, as both chips 35 and 45, Ir alloy chips having a high melting point and excellent in wear resistance to which at least one of Rh, Pt, Ru, Pd and W is added with Ir as a main component are adopted. Yes.
[0043]
Moreover, the welding structure of the center electrode side chip | tip 35 and the center electrode 30 among these both chips | tips 35 and 45 can employ | adopt what was formed by the method as described in the above-mentioned conventional gazette. The cross-sectional configuration is schematically shown in FIG.
[0044]
As shown in FIG. 3, when the cross section along the axial direction of the tip 35 in the melting part 37 is viewed, the side surface 35a of the tip 35 and the tip surface of the center electrode 30 (joint surface of the noble metal tip in the electrode base material) 31 are formed. The outer surface 37a of the fusion | melting part 37 to connect is linear.
[0045]
On the other hand, the welding structure of the ground electrode side tip 45 and the ground electrode 40 has the following unique configuration in the present embodiment. FIG. 4 is a diagram showing a schematic cross-sectional configuration of the welding structure on the ground electrode 40 side.
[0046]
The ground electrode side tip 45 whose one end side is laser welded to the side surface 43 of the tip end portion of the ground electrode 40 has a cross-sectional area of 0.12 mm at the tip end surface on the other end side. ² 1.15mm above ² The protrusion length L from the tip end side surface 43 of the ground electrode 40 is not less than 0.3 mm and not more than 1.5 mm. In this example, a cylindrical shape having a diameter D of 0.4 mm or more and 1.2 mm or less is formed corresponding to the cross-sectional area range.
[0047]
The outer surface connecting the side surface 45a of the tip 45 and the side surface of the tip portion of the ground electrode 40 (joint surface of the tip of the ground electrode) 43 in the melted portion (melted and fixed layer) 47 in which the ground electrode 40 and the tip 45 are melted together. 47a has a curved surface shape that has a radius of curvature R and is recessed.
[0048]
The shape of the melted portion 47 on the ground electrode 40 side having such a curvature radius R can be formed as follows. FIG. 5 is an explanatory view showing the welding method of the ground electrode side tip 45 and the ground electrode 40 in a schematic cross section. First, the one end surface 45b of the ground electrode side chip 45 is brought into contact with the tip end side surface (surface of the ground electrode) 43 without being buried in the ground electrode 40 (FIGS. 5A to 5C).
[0049]
Subsequently, the side surface 45a of the tip 45 and the tip portion side surface 43 are oblique with respect to the corner portion 49 formed by the side surface 45a of the tip 45 extending outward from the tip portion side surface 43 and the tip portion side surface 43. Laser irradiation is performed from the direction (the direction of the white arrow in the figure) to melt the chip 45 and the ground electrode 40, thereby forming the melted portion 47 (FIGS. 5D and 5E).
[0050]
In this way, a welded structure between the ground electrode side tip 45 and the ground electrode 40 through the melting portion 47 shown in FIG. 4 is appropriately formed. For example, after that, the ground electrode 40 is fixed by welding to the mounting bracket 10, the center electrode 30 covered with the insulator 20 is installed in the mounting bracket 10, and the ground electrode 40 is deformed to discharge. By forming the gap 50, the spark plug S1 shown in FIG. 1 is manufactured.
[0051]
Next, the cross-sectional area of the tip surface on the other end side laser-welded in the ground electrode side tip 45 is 0.12 mm. ² 1.15mm above ² Hereinafter, the grounds for setting the protrusion length L to 0.3 mm or more and 1.5 mm or less will be described.
[0052]
It is considered that the noble metal tip is less likely to inhibit the growth of flame nuclei generated in the discharge gap as the diameter thereof is thinner and the protrusion length from the ground electrode is longer. Therefore, the following judgment test was performed on the diameter of the noble metal tip and the protruding length from the ground electrode that can ensure good ignitability without inhibiting the growth of the flame kernel.
[0053]
The spark plug S1 with various D and L changes is attached to the engine, and the determination method is to increase the air-fuel ratio at the idling air-fuel ratio and to generate an ignition error twice or more in 2 minutes. Was defined as a limit value (ignition limit air-fuel ratio). The evaluation engine was a 4-cylinder 1.6 liter engine with an engine speed of 650 rpm.
[0054]
Although not limited, as the center electrode side chip 35 in this determination test, for example, the diameter D ′ is 0.4 mm, and the protruding length L ′ from the tip surface 31 of the center electrode 30 is 0.6 mm. A certain cylindrical body (see FIG. 3) was used, and the discharge gap 50 was 0.7 mm.
[0055]
The test results are shown in FIG. A larger ignition limit air-fuel ratio means that more lean combustion is possible and ignitability is improved. As can be seen from FIG. 6, the ignitability is improved as the diameter D of the ground electrode side tip 45 is reduced, but the ignitability is significantly reduced when the diameter D is increased to 1.3 mm.
[0056]
In addition, the ignitability is improved as the protruding length L of the ground electrode side chip 45 is increased, but the degree of improvement is approximately 0.3 mm or more and is substantially saturated. Therefore, from FIG. 6, as the ground electrode side chip 45 capable of ensuring good ignitability, the diameter D is 1.2 mm or less (the cross-sectional area is 1.15 mm). ² It is understood that the protrusion length L from the ground electrode is required to be 0.3 mm or more.
[0057]
Moreover, even with the ground electrode side tip 45 made of a noble metal having excellent heat resistance and wear resistance, the diameter D is 0.4 mm (the cross-sectional area is 0.12 mm). ² If it is thinner, sparks concentrate and the wearability deteriorates. On the other hand, if the protruding length L from the ground electrode 40 is longer than 1.5 mm, the temperature at the tip of the tip 45 rises greatly and the tip 45 is likely to melt.
[0058]
For these reasons, in the present embodiment, the ground electrode side tip 45 has a cross-sectional area of the tip end surface on the other end side, which is laser-welded, of 0.12 mm. ² 1.15mm above ² It is assumed that the diameter D is 0.4 mm or more and 1.2 mm or less in this example, and the protruding length L is 0.3 mm or more and 1.5 mm or less. Thereby, ignitability can be ensured appropriately.
[0059]
Next, in the melted portion 47 where the ground electrode 40 and the tip 45 are melted together, the outer surface 47a connecting the side surface 45a of the tip 45 and the tip end side surface 43 of the ground electrode 40 is recessed with a radius of curvature R. The basis for the shape will be described.
[0060]
When the ground electrode side tip and the ground electrode are laser welded by the method described in the above-mentioned conventional publication, the welded structure is the same as that of the center electrode 30 shown in FIG.
[0061]
That is, as shown in FIG. 7, also in the ground electrode 40, the outer surface 47 a of the melting portion 47 connecting the side surface 45 a of the chip 45 and the tip end side surface 43 of the ground electrode 40 is linear. In this case, in the ground electrode 40 in which the temperature at the time of use is higher than that of the center electrode 30, the bondability between the ground electrode 40 and the chip 45 does not satisfy the practical level, and peeling occurs from the joint at the time of use. There is a high possibility that the chip 45 will fall off.
[0062]
If the shape of the melted portion 47 on the ground electrode 40 side is a curved shape having a radius of curvature R as described above with respect to such a melted portion shape, joining at the melted portion 47 is required. The melting part 47 can be made as thin as possible while securing the volume.
[0063]
Further, in the conventional shape as shown in FIG. 7, bending points exist at the interface between the tip 45 and the melting part 47 and at the interface between the melting part 47 and the tip side surface 43 of the ground electrode 40, and strong heat is generated at that point. Stress is generated. On the other hand, as shown in FIG. 4, since the outer surface 47a of the melting portion 47 has the curved surface, the surface extending from the tip 47 to the melting portion 47 and the ground electrode 40 is configured with a smooth curve. Such stress concentration is considered to be avoided.
[0064]
Therefore, according to the present embodiment, it can be said that the thermal stress generated in the melting portion 47 can be reduced, and the bondability between the ground electrode 40 and the chip 45 can be improved.
[0065]
Here, as a standard of how much the thermal stress generated in the melted portion 47 on the ground electrode 40 side is reduced, for example, heat generated in a structure in which the laser welding structure according to the above-described conventional method is applied to the center electrode. The stress, that is, the thermal stress (center electrode side thermal stress) generated in the melting portion 37 on the center electrode 30 side in the spark plug S1 of the present embodiment can be employed.
[0066]
This is because, in the spark plug S1, the bondability between the electrode and the chip can be ensured at a practical level on the center electrode 30 side. Then, regarding the thermal stress (ground electrode side thermal stress) generated in the melted portion 47 when the radius of curvature R is changed in the melted portion 47 on the ground electrode 40 side, FEM based on the central electrode side thermal stress as a reference. (Finite element method) analysis was performed.
[0067]
The result of thermal stress analysis of this melted part is shown in FIG. Here, when obtaining the thermal stresses on the center electrode side and the ground electrode side, the tip diameters D and D ′ are 1.2 mm, the protruding lengths L and L ′ are 1.0 mm, and the tip components of the melting portions 37 and 47 are set. Was 35% by weight. This is the strictest specification in terms of bondability. Further, the site where the thermal stress was generated was a site near the electrodes 30 and 40 in the melted portions 37 and 47.
[0068]
In FIG. 8A, the ground electrode side thermal stress when the radius of curvature R is changed is shown as a stress level ratio which is a value obtained by normalizing the center electrode side thermal stress level to 1. In addition, the “conventional shape” in FIG. 8A is the shape shown in FIG. 7, and the generated thermal stress is the same as the melted part shape of the melted part 35 on the center electrode 30 side. large. This is because the temperature of the ground electrode 40 (for example, 900 ° C.) is higher than the temperature of the center electrode 30 (for example, 800 ° C.) during use.
[0069]
In FIG. 8A, if the radius of curvature R is such that the stress level ratio is 1 or less, the bondability between the ground electrode 40 and the ground electrode side tip 45 is higher than that of the conventional melted part shape. It can be said that the level of practical use has been improved. That is, the radius of curvature R in the melted portion 47 on the ground electrode 40 side is preferably 0.1 mm or greater and 1.0 mm or less.
[0070]
According to FIG. 8A, when the curvature radius R is smaller than 0.1 mm or larger than 1.0 mm, the ground electrode side thermal stress exceeds the level of the center electrode side thermal stress. ing. This is because if the radius of curvature R is smaller than 0.1 mm, the shape of the melted portion becomes steep and thermal stress tends to concentrate, and if the radius of curvature R is larger than 1.0 mm, the radius of curvature R is too large. This is probably because the difference from the shape of the melted portion becomes smaller and the merit of having the curvature radius R is lost.
[0071]
From the above, in the present embodiment, on the ground electrode 40 side, the outer surface 47a of the melting part 47 connecting the side surface 45a of the ground electrode side chip 45 and the tip end side surface 43 of the ground electrode 40 has a radius of curvature R. It has a curved shape that is concave. The curvature radius R is preferably 0.1 mm or greater and 1.0 mm or less.
[0072]
Further, FIG. 8B is a diagram showing a cross section of the ground electrode side tip 45 in contact with the ground electrode 40. When the ground electrode side tip 45 is actually laser welded to the ground electrode 40, the radius of curvature is shown. If R is to be reduced, the penetration depth d of the melting part 47 is not sufficient.
[0073]
It has been experimentally confirmed that the penetration depth d of the melted portion is required to be D / 4 or more from the viewpoint of securing the bondability between the ground electrode side chip 45 and the ground electrode 40. Here, D is the maximum width of the cross section in contact with the ground electrode 40 of the ground electrode side chip 45 as shown in FIG. 8B, but in this example, the ground electrode side chip 45 having a cylindrical shape is used. Corresponds to the diameter of.
[0074]
However, if the penetration depth d is increased, the welding energy increases, and the nugget width W shown in FIG. 8B increases. Then, the curvature radius R also becomes large, and the merit of attaching the curvature radius R becomes small. On the other hand, if the radius of curvature R is to be reduced, the nugget width W is also reduced, and the penetration depth d is also reduced, making it difficult to secure the bondability.
[0075]
Therefore, the value of the minimum required penetration depth d, that is, the radius of curvature R when d = D / 4 is the lower limit value for securing the bondability. D of the ground electrode side tip 45 of this example is 0.4 mm or more and 1.2 mm or less. When the radius of curvature R when d = D / 4 is obtained for D in this range, R = D / 4 (D × 1/4).
[0076]
Further, from the result of FEM analysis, in order to exhibit the merit of adding the radius of curvature R, the D is preferably 3D / 4 (D × 3/4) or less. Therefore, in order to ensure the bondability of the noble metal tip while exhibiting the effect of the curvature radius R, the maximum width of the cross section in contact with the ground electrode 40 of the ground electrode side tip 45 is D / 4 or more and 3D. / 4 or less is preferable.
[0077]
In the present embodiment, the tip of the above-described Pt, Pt alloy, Ir, Ir alloy or the like is adopted as the ground electrode side tip 45. In this case, the component of the tip 45 in the melting portion 47 is 35. It is preferable that the weight is not less than 80% by weight.
[0078]
This is based on the examination results described below. The melted portion 47 is formed by melting the ground electrode side tip 45 and the ground electrode (Ni-based alloy) 40, and therefore, the bonding property varies depending on the melt composition. Therefore, an FEM analysis was performed on the relationship between the components of the ground electrode side tip 45 and the thermal stress in the melting portion 47.
[0079]
An example of the analysis result is shown in FIG. FIG. 9 is an example in which the Ir alloy tip is adopted as the ground electrode side tip 45, and the Ir alloy component ratio (% by weight) in the melted portion 47 and the stress level ratio (center electrode side thermal stress is set to 1). The relationship with the ground electrode side thermal stress value) is shown. Further, as for the ground electrode side thermal stress, the point a (interface portion between the chip and the melted portion) and the point b (interface portion between the melted portion and the ground electrode) in the melted portion 47 in FIG. , A point is shown as a black circle plot, and b point is shown as a white circle plot.
[0080]
Here, in FIG. 9 as well, the center electrode side thermal stress is used as a reference. In this case, the diameters D and D ′ and the projecting lengths L and L ′ of both the chips 35 and 45 have the same dimensions. Further, the tip component of the melted portion 37 on the center electrode 30 side was set to a lower limit value (35% by weight in this example) that satisfies a practical level of bondability on the center electrode 30 side. The material of the chips 35 and 45 is not limited, but in this example, Ir is 90% by weight and Rh is 10% by weight.
[0081]
From FIG. 9, in order to set the thermal stress at the point a (interface between the chip and the melted portion) side to be equal to or lower than the reference central electrode side thermal stress, 35% by weight or more is preferable, and the point b (melted point) It can be seen that 80% by weight or less is preferable in order to set the thermal stress on the side of the interface between the part and the ground electrode to the reference center electrode side thermal stress or less.
[0082]
The ground electrode side tip 45 protrudes to the discharge gap 50 side from the ground electrode 40, and the temperature is higher than the ground electrode (electrode base material) 40. However, the generated thermal stress is larger than the interface between the melting portion 47 and the ground electrode 40. For this reason, in adjusting the tip component ratio of the melting portion 47, it is considered preferable to adjust the portion near the tip 45.
[0083]
As described above, according to the present embodiment, as described above, by adopting the laser welding structure in which the dimensions D and L of the ground electrode side tip 45 and the shape of the melting portion 47 are defined, the ignitability is achieved. Thus, it is possible to provide a spark plug in which the bondability between the ground electrode and the noble metal tip is improved while ensuring the above.
[0084]
Moreover, according to this embodiment, the laser welding structure of this embodiment can be manufactured appropriately by the manufacturing method shown in FIG. In addition, according to the present manufacturing method, as described in the above-mentioned conventional publication, it is not necessary to process the electrode base material to form a small diameter portion or to embed a noble metal tip in the electrode base material. It can be set as a simple manufacturing method.
[0085]
(Other embodiments)
In addition to the main ground electrode 40 that forms the spark gap, that is, the discharge gap 50, as shown in FIG. 10, the present invention includes a sub-ground electrode 40 a that faces the tip 21 of the insulator 20. The present invention can also be applied to a spark plug having the same. Here, in FIG. 10, (a) is the figure which looked at the spark discharge part from the side surface direction of the main ground electrode 40, (b) is an A arrow view of (a).
[0086]
In the spark plug shown in FIG. 10, if the same configuration as the above embodiment is adopted for the main ground electrode 40 and the noble metal tip 45 laser-welded to the main ground electrode 40, the ground electrode and the ground electrode It is possible to provide a spark plug that improves the bondability with a noble metal tip and also ensures carbon fouling resistance.
[0087]
In addition, when the base material of the ground electrode 40 in the above embodiment is a Ni-base alloy such as Inconel 600 (registered trademark) with 1.5% by weight or more of Al added, it has high ignitability and heat resistance. A spark plug having excellent oxidation resistance can be provided.
[0088]
Further, in order to improve the heat resistance and oxidation resistance, as shown in FIG. 11 (a), a Cu material 40b as a good heat conducting material is provided inside, and the Cu material 40b is a coating material made of a Ni-based alloy. The ground electrode 40 may be covered with 40c. Furthermore, as shown in FIG. 11 (b), the good heat conductive material has a two-layer structure in which a Ni material 40d is coated with a Cu material 40b as a core material, and this is covered with a coating material 40c. The electrode 40 may be used.
[Brief description of the drawings]
FIG. 1 is a half sectional view showing an overall configuration of a spark plug according to an embodiment of the present invention.
FIG. 2 is an enlarged configuration diagram in the vicinity of a discharge gap in the spark plug shown in FIG. 1;
FIG. 3 is a schematic cross-sectional view showing a tip welding structure on the center electrode side in the spark plug shown in FIG. 1;
4 is a schematic cross-sectional view showing a tip welding structure on the ground electrode side in the spark plug shown in FIG. 1. FIG.
FIG. 5 is an explanatory view showing a welding method between a ground electrode side tip and a ground electrode.
FIG. 6 is a diagram showing an analysis result on the relationship between the shape of the ground electrode side tip and the ignitability.
FIG. 7 is a schematic cross-sectional view showing a conventional shape in a tip welding structure on the ground electrode side.
FIG. 8A shows the thermal stress generated in the melted portion when the radius of curvature R is changed.
(B) shows the penetration depth d and the nugget width W of the melted part.
FIG. 3 is a diagram showing a cross section in contact with a ground electrode of a noble metal tip in order to represent
FIG. 9 shows the analysis result of the relationship between the composition of the Ir alloy chip and the thermal stress in the molten part.
FIG.
FIG. 10 shows a spark lamp as another embodiment of the present invention having a main ground electrode and a sub-ground electrode.
It is a figure which shows the principal part of a lug.
FIG. 11 shows a spar as another embodiment of the present invention having a ground electrode having a plurality of layer structures.
It is a schematic sectional drawing which shows the principal part of a cuprag.
[Explanation of symbols]
30 ... Center electrode, 40 ... Ground electrode, 43 ... Side surface of the tip of the ground electrode,
45: Ground electrode side chip, 45a: Side surface of ground electrode side chip,
45b ... one end surface of the ground electrode side chip, 47 ... a melting part on the ground electrode side,
47a: the outer surface of the fusion part connecting the side surface of the ground electrode side tip and the side surface of the tip of the ground electrode, 50: discharge gap

Claims (7)

A center electrode (30) and a ground electrode (40) arranged opposite to each other via a discharge gap (50);
In a spark plug comprising a noble metal tip (45) laser welded to a portion (43) facing the discharge gap in the ground electrode,
The noble metal tip has one end side of the laser-welded to the ground electrode, the sectional area of the distal end surface of the other end side 0.12 mm ² or more 1.15 mm ² or less was in projection length from said ground electrode (L) Is 0.3 mm or more and 1.5 mm or less,
In the melting part (47) in which the ground electrode and the noble metal tip are melted together, an outer surface (47a) connecting the side surface (45a) of the noble metal tip and the joint surface (43) of the noble metal tip in the ground electrode, A spark plug having a concave curved shape and having a radius of curvature (R) of 0.1 mm to 1.0 mm .   The curvature radius (R) is D / 4 or more and 3D / 4 or less, where D is the maximum width of the cross section of the noble metal tip (45) contacting the ground electrode (40). Item 2. The spark plug according to item 1.   The spark according to claim 1 or 2, wherein the noble metal tip (45) is an alloy containing Ir as a main component and at least one of Rh, Pt, Ni, W, Pd, Ru, and Os added thereto. plug.   The noble metal tip (45) is mainly composed of Ir, 50% by weight Rh, 50% by weight Pt, 40% by weight Ni, 30% by weight W, 40% by weight Pd, 30% or less. The spark plug according to claim 3, wherein the spark plug is an alloy to which at least one of Ru of not more than wt% and Os of not more than 20 wt% is added.   The spark according to claim 1 or 2, wherein the noble metal tip (45) is an alloy containing Pt as a main component and at least one of Ir, Ni, Rh, W, Pd, Ru, and Os added thereto. plug.   The noble metal tips (50, 60) are mainly composed of Pt, 50 wt% or less of Ir, 40 wt% or less of Ni, 50 wt% or less of Rh, 30 wt% or less of W, or 40 wt% or less of Pd. The spark plug according to claim 5, wherein the spark plug is an alloy to which at least one of Ru of 30 wt% or less and Os of 20 wt% or less is added.   The spark plug according to any one of claims 3 to 6, wherein a component of the noble metal tip (45) in the melting part (47) is not less than 35 wt% and not more than 80 wt%.

Images